Preparation and dynamic properties of an anisotropic natural rubber film as viewed by electron spin resonance–spin probe method

Natural rubber (NR) films with the thickness of about 1 mm were prepared by removing the liquid phase from NR latex, which was previously irradiated. The primary radiation dose varied from 0 kGy (for unirradiated NR) to 200 kGy. Dry NR films were uniaxially stretched, and the degree of deformation, defined as = l/l(0) (l(0) and l being the lengths of relaxed and uniaxially deformed sample, respectively), was varied from = 1.0 (relaxed state) to = 2.7. Samples were then irradiated with secondary dose, which was chosen to be 100 or 200 kGy. NR films were characterized by differential scanning calorimetry and electron spin resonance-spin probe method. In addition, samples were exposed to accelerated thermal aging, and changes in molecular dynamics and structure were obtained. It has been shown that the application of deformation during the cross-linking leads to the restriction in segmental mobility for the lower secondary dose, whereas for the higher secondary dose, larger values of induce an opposite effect originating from the structural changes. Thermally aged samples show higher amount of the gel phase and consequently higher fraction of slow motional chain segments. POLYM. ENG. SCI., 53:2284-2291, 2013. (c) 2013 Society of Plastics Engineers